PPC: Reland Vector ICs: platform support for vector-based stores.

PPC: Reland Vector ICs: platform support for vector-based stores.

Port 40fbed0609ddb3e4ee4338049383004b62d13853

Original commit message:
    The last changes for vector store functionality, they are in 3 areas:

    1) The new vector [keyed] store code stubs - implementation.
    2) IC and handler compiler adjustments
    3) Odds and ends. A change in ast.cc, a test update, a small Oracle fix.

R=mvstanton@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, dstence@us.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1330883002

Cr-Commit-Position: refs/heads/master@{#30657}